In the copending application of co-inventor George R. Mather, Jr., Ser. No. 549,291, filed Feb. 12, 1975 (now U.S. Pat. No. 4,002,160), there is disclosed an array of similar multiple glass solar energy collector tubes connected in a manifold and supported parallel to each other between the sun and a diffuse planar reflecting surface. The tubes are parallel to the reflecting surface and spaced a distance no more than four times the tube outside diameters of the collector tubes from the planar diffuse reflector and spaced apart center-to-center of the tubes a distance no more than four times such outside diameter dimension. Approximately half the sunlight falling between the collector tubes and reaching the diffuse reflecting surface is reflected to the tube undersides. Comparing this array to an array of close packed tubes, the spaced array contains half as much hardward (tubes, etc.) but delivers about the same amount of energy under most operating conditions. Inasmuch as the diffuse reflecting surface of planar design is significantly less expensive than the collector tubes eliminated in the spacing recommended, a highly cost-effective collector system is achieved.
However, this diffuse reflector array has solar intercept efficiencies in the range of 50-60%, depending upon the time of solar day, because approximately half the light incident to the reflecting surface is not reflected to the lower surface of the parallel collector tubes. If this light is collected, the resultant intercept efficiency would approach 80%. Additionally, an increase in tube spacing of the array would lead to even lower effective loss coefficients and therefore to further improvements in performance at higher temperatures.